Toner is a fine, polymer-based powder which has electrical charge or possessing magnetic properties. It is widely used in laser printers, photocopiers and fax devices, which are based on electrophotographic technology invented more than 35 years ago. Toner starts off as a powder, and passes through these electrophotographic machines being heated to melt and ends up as a solid bonded to the printed paper as it is cooled down.
The conventional toner is made by compounding the ingredients, such as resins, pigments, magnetic iron oxides, waxes and charge control agents (CCA) by melting and blending the ingredients to form a paste. This mixture is then cooled by extruding onto a cooling belt into thin sheet or plate. The raw toner is then pelletized and ground into a fine powder within a controlled particle size range by jet mills or air-swept hammer mills. This process resulted in toner granules of various sizes and jagged shapes when viewed under a microscope. The over-size and under-size toner particles are sieved out. The pulverized powder is then blended with additives to adjust flow and electrostatic properties.
Particle size has significant effect on the toner performance. Finer size and more uniform shapes enable more accurate colour reproduction and more efficient toner use. Smaller laser beam dots and smaller toner particles could give better print quality. With the conventional process, the energy costs for production of smaller particles increase exponentially with smaller particle size.
CPT, the chemically produced toner, is also known as polymerization toner. Compared to conventional toners, it provides advantages such as developed by a simpler manufacturing process with the potential for a lower unit manufacturing cost and potential for lower capital investment in manufacturing plant. Besides, it provides improved print performance as it is capable of producing smaller and more uniform toner particles with better fixing and color performance. In particular, the CPT can be conveniently made from an emulsion polymer through emulsion polymerization process.
The particle size of CPT can be controlled by the reaction conditions such as stirring rate, surfactant concentration, temperature, mode and order of addition, core-shell formation and others. Additionally, CPT toners have a more uniform shape and can provide sharper imaging. They can be used in both monochrome and color applications.
Owing to the advantages provided by the CPT, researches into the creation of CPT have begun more than 30 years ago. The chemical processes involved have been directed towards the synthesis of the major component of the toner, which is the polymer binder or more specifically the toner resin. Polymerization methods for creating the toner resin can include suspension, dispersion, emulsion and core-shell or microencapsulation.
The most popular process for synthesizing CPT is the EA process, in which a polymer is first prepared by emulsion polymerization. The emulsion produced is further added with other required components such as CCA, wax and pigment, in very fine suspensions, followed by a water soluble coagulant or flocculating agent, and the temperature is adjusted close to the class transition temperature (Tg) of the polymer to cause aggregation of the polymer particles and the other components to form particles of desirable sizes. While maintaining the stirring at certain speed, the temperature is raised higher, usually above the Tg, to cause the aggregated particle to coalesce into smooth particle of regular shape. Subsequently, the temperature is reduced to allow solidification of the particles. They are then washed and dried to become the raw toner before being made into the final toner particles through the final additives blending step.
Many manufacturing processes of CPT have been based on the concept of EA and the products thereof have been patented in the prior arts, each with a different improvising approach and characteristic. For example, the U.S. Pat. No. 5,405,728 of Xerox Corporation discloses a toner manufactured by the EA technique whereby a counterionic surfactant is used to facilitate the aggregation to form the toner particles.
Disclosed in U.S. Pat. No. 6,251,556 is an invention of Fuji Xerox describing a toner made from a binder resin having a low molecular weight polymer obtained by emulsion polymerization of an unsaturated monomer or mixture of monomers at a temperature of 115° C. or higher in the presence or absence of a chain transfer agent.
U.S. Pat. No. 6,942,954 also describes an EA process involving heating a mixture of a magnetite dispersion, a colorant dispersion, a wax dispersion, a first latex containing a crosslinked resin, and a second latex containing a resin free of crosslinking in the presence of a coagulant to provide aggregates, stabilizing the aggregates with a silicate salt dissolved in a base, and further heating the aggregates to provide coalesced toner particles.
In the U.S. Pat. No. 7,344,819 filed on 24 Nov. 2004, belonging to Brother Kogyo Kabushiki Kaisha, a method for manufacturing toner includes the steps of combining a polymer resin and an organic solvent to obtain an oil-based solution; combining a dispersion stabilizer with water to obtain a water-based solution; adding an amphiphilic surfactant solvent to the water-based solution; emulsifying the oil-based solution in the water-based solution to form emulsion; and removing the organic solvent from the emulsion particles, which can then be used for manufacture of toner by the EA process.
Seeing the existing CPT disclosed by the prior arts are made from entirely petrochemicals which are derived from the non-renewable resources, and are non-sustainable, it is desirable for the present invention to provide a toner based on naturally derived materials, such as natural oils, particularly palm oils. More specifically, the use of palm oil-based unsaturated polyester resins, which could be easily copolymerized with other monomers to produce CPT, shall be a more environmental friendly approach as compared to the manufacture of CPT from 100% petrochemicals. There is also a need to provide a naturally derived product which is lower in cost yet comparable in quality to reduce the use of additives which are petrochemicals or toxic compounds, such as wax and CCA in the toner synthesis.